Liquid alkoxysilyl-functional silicone resins, method for their preparation, and curable silicone resin compositions

ABSTRACT

Liquid alkoxysilyl-functional silicone resins having excellent storage stability and a method of preparing these liquid alkoxysilyl-functional silicone resins comprising running an equilibration polymerization reaction with components comprising (A) a polydiorganosiloxane and (B) an alkyl polysilicate in the presence of (C) an equilibration polymerization catalyst. Curable silicone resin compositions comprising the aforesaid liquid alkoxy-functional silicone resins which have excellent curability and when cured form a water-repellent coating on a variety of substrate surfaces.

This invention relates to liquid alkoxysilyl-functional silicone resinshaving excellent storage stability and a method of preparing theseliquid alkoxysilyl-functional silicone resins comprising running anequilibration polymerization reaction with components comprising (A) apolydiorganosiloxane and (B) an alkyl polysilicate in the presence of(C) an equilibration polymerization catalyst. This invention alsorelates to curable silicone resin compositions comprising the aforesaidliquid alkoxy-functional silicone resins which have excellent curabilityand when cured form a water-repellent coating on a variety of substratesurfaces.

BACKGROUND OF THE INVENTION

Solventless low-viscosity alkoxysilyl-functional silicone resins havingdifunctional and trifunctional siloxane units are known (see U.S. Pat.No. 4,929,691). These liquid alkoxysilyl-functional silicone resins areobtained by hydrolyzing the product from an equilibration reactionbetween polydimethylsiloxane and methyltrialkoxysilane. While theseresins can form water-repellent coatings, their curability cannot beconsidered satisfactory, and in particular their curability at roomtemperature is unacceptable.

Compositions comprising, for example, tetraalkoxysilane blended inmethyl polysilicate are known as polysilicate-type coating compositions(see Japanese Patent Application Publication (Kokai) No. Hei 3-239774(239,774/1991)). However, the cured coatings afforded by thesecompositions exhibit an unsatisfactory water repellency.

An object of this invention is to provide liquid alkoxysilyl-functionalsilicone resins that exhibit excellent storage stability. Another objectof this invention is to provide a method for the preparation of theseliquid alkoxysilyl-functional silicone resins. Yet another object ofthis invention is to provide curable silicone resin compositions thatexhibit excellent curability and when cured form a water-repellentcoating on a variety of substrate surfaces.

THE INVENTION

This invention relates to liquid alkoxysilyl-functional silicone resinshaving excellent storage stability and a method of preparing theseliquid alkoxysilyl-functional silicone resins comprising running anequilibration polymerization reaction with components comprising (A) apolydiorganosiloxane and (B) an alkyl polysilicate in the presence of(C) an equilibration polymerization catalyst. This invention alsorelates to curable silicone resin compositions comprising the aforesaidliquid alkoxy-functional silicone resins which have excellent curabilityand when cured form a water-repellent coating on a variety of substratesurfaces.

One embodiment of the present invention is a method comprising runningan equilibration polymerization reaction with components comprising (A)a polydiorganosiloxane and (B) an alkyl polysilicate in the presence of(C) an equilibration polymerization catalyst to form liquidalkoxysilyl-functional silicone resins.

The silicon-bonded organic groups in the polydiorganosiloxane (A) can beexemplified by alkyl groups such as methyl, ethyl, and propyl; alkenylgroups such as vinyl, allyl, and 5-hexenyl; aryl groups such as phenyl;and halogenated alkyl groups such as 3,3,3-trifluoropropyl andnonafluorohexyl. Component (A) itself can be exemplified bypolydimethylsiloxanes, dimethylsiloxane-phenylmethylsiloxane copolymers,and dimethylsiloxane-diphenylsiloxane copolymers. The molecularstructure of component (A) can be straight chain or cyclic. In the caseof the straight-chain polyorganosiloxanes, excessively high viscosities(as measured at 25° C.) should be avoided, and these straight-chainpolydiorganosiloxanes can be exemplified by trialkylsiloxy-endblocked(e.g., trimethylsiloxy-endblocked) polydimethylsiloxanes with a degreeof polymerization no greater than 100. The cyclic polydiorganosiloxanescan be exemplified by the tetramer (ie. having 4 SiO— groups) to the30-mer (having 30 SiO— groups). Component (A) is preferably astraight-chain or cyclic polydimethylsiloxane and is more preferably acyclic polydimethylsiloxane. Component (A) can also comprise mixtures ofpolydimethylsiloxanes having different degrees of polymerization.

The alkyl polysilicate (B) useful in the present method comprisespolysiloxanes having alkoxy groups bonded to the silicon atoms in themolecule. Component (B) is ordinarily synthesized by the partialhydrolysis and condensation of a tetraalkoxysilane. The alkoxy group canbe exemplified by methoxy, ethoxy, propoxy, and isopropoxy, with methoxybeing preferred. Examples of component (B) include methyl polysilicate(which is the partial hydrolysis and condensation product oftetramethoxysilane) and ethyl polysilicate (which is the partialhydrolysis and condensation product of tetraethoxysilane). Preferably,component (B) is a mixture of polysiloxanes ranging from the dimer tothe 100-mer and more preferably is a mixture of polysiloxanes rangingfrom the dimer to the 20-mer. Component (B) is preferably added in anamount from 10 to 1,000 weight parts and more preferably in an amountfrom 20 to 500 weight parts, in each case per 100 weight parts ofcomponent (A). The molar ratio of component (A) to component (B) isgenerally from 1:0.1 to 1:10 and preferably is 1:0.2 to 1:5.

The equilibration polymerization catalyst (C) accelerates theequilibration polymerization reaction of component (A) and component(B). Basic catalysts and acid catalysts generally used for theequilibration of siloxanes can be used as component (C). Examples ofcomponent (C) include basic catalysts such as potassium hydroxide,potassium silanolate, trimethylammonium hydroxide, and trimethylammoniumsilanolate and acid catalysts such as trifluoromethanesulfonic acid,activated clay, and concentrated sulfuric acid. The acid catalysts arepreferred for component (C).

Component (C) is added in a catalytic quantity, with a range of 0.0001to 5 weight parts per 100 weight parts component (A) being preferred anda range of 0.001 to 0.5 weight part per 100 weight parts component (A)being more preferred.

Optionally, a functional alkoxysilane (D) having the general formulaR¹SiR_(n)(OR²)₃-n may be included in the equilibration step along withcomponents (A), (B), and (C). R¹ in this general formula is a C₁ to C₁₀monovalent organic group containing an aliphatically unsaturated bond.Examples of R¹ include vinyl, allyl, 5-hexenyl, 3-methacryloxypropyl,2-methacryloxyethyl, 3-acryloxypropyl, and 2-acryloxyethyl, with3-methacryloxypropyl being preferred. Each R² in the preceding generalformula is a C₁ to C₁₀ alkyl group. Examples of R² include methyl,ethyl, propyl, or octyl, with methyl being preferred. Each R in thepreceding general formula is a substituted or unsubstituted C₁ to C₁₀monovalent hydrocarbyl group. Examples of R² include alkyl groups suchas methyl, ethyl, propyl, and hexyl and alkenyl groups such as vinyl andallyl. The subscript n in the preceding general formula is 0 to 2.Examples of component (D) include vinyltrimethoxysilane,vinylmethyldimethoxysilane, allyl trimethoxysilane,3-acryloxypropyltrimethoxysi lane, 3-acryloxypropylmethyldimethoxysilane, and 3-methacryloxypropyltrimethoxysi lane.

Component (D) is preferably added in an amount from 0.5 to 100 weightparts per 100 weight parts component (A) and more preferably in anamount from 1 to 50 weight parts per 100 weight parts component (A).

The equilibration polymerization reaction can be run by mixingcomponents (A), (B), (C), and optionally (D), heating the mixture intothe temperature range in which component (C) is active, for example, 50to 200° C., and allowing the components to react, typically for 1 to 10hours. This equilibration polymerization reaction results in anequilibration among the siloxane bonds in component (A), the siloxaneand silicon-alkoxy bonds in component (B), and the silicon-alkoxy bondsin component (D). This equilibration need not proceed to a state ofcomplete or total equilibration, and it may provide a state in whichonly a certain degree of exchange (equilibration) has been achieved.Some component (A), (B), and/or (D) may therefore remain presentpost-reaction forming a mixture.

In a preferred embodiment, the present method further comprisesthermally removing low-molecular-weight volatile siloxanes such aslow-molecular-weight portion of alkoxysilyl-functional silicone resinsgenerated as by-products in the equilibration step or remainingcomponent (A) such as volatile cyclic diorganosiloxanes. Cyclicdiorganosiloxane tetramer to decamer, which are volatile species, aredesirably removed because these species do not promote the curingreaction of the alkoxysilyl-functional silicone resin. It isparticularly preferred that the content of the cyclic diorganosiloxanetetramer, which is produced in large amounts, be brought to 1 weight %or less. These volatile cyclic diorganosiloxanes should be dischargedand removed from the system by accelerating their evaporation, asnecessary or desired by heating under reduced pressure.

Once the equilibration polymerization reaction has reached the desiredpoint and prior to thermally removing the low-molecular-weight volatilesiloxanes, it is preferred to deactivate the equilibrationpolymerization catalyst to minimize any further re-equilibration. Whenthe equilibration reaction has been run using a basic catalyst, catalystdeactivation can be achieved by neutralization by mixing in anequivalent amount of an acidic substance, for example, carbon dioxide orhydrogen chloride. When the equilibration reaction has been run using anacid catalyst, catalyst deactivation can be achieved by neutralizationby mixing in an equivalent amount of a basic substance, for example,sodium bicarbonate, sodium carbonate, or sodium hydroxide. When thecatalyst is thermally decomposable, it can be decomposed by raising thetemperature by heating. Deactivation of this equilibrationpolymerization catalyst can be carried out before or after removal ofthe volatile siloxanes. After the basic or acid catalyst has beensatisfactorily deactivated by neutralization, the neutralization salttherefrom can remain in the reaction solution as the volatile siloxanesis thermally removed or can be removed from the reaction solution by,for example, filtration.

In a preferred embodiment the present method further comprises partiallyhydrolyzing the liquid alkoxysilyl-functional silicone resins to adjustthe amount of alkoxy in the molecule after thermally removing thelow-molecular-weight volatile siloxanes. The amount of water addedshould be less than the number of moles necessary for hydrolysis of thealkoxy groups in component (B). Catalysts known in the art to promotecondensation reactions can also be added to this step. Examples of thesecondensation reaction-promoting catalysts include organotin compoundssuch as dibutyltin diacetate, dibutyltin dioctate, dibutyltin dilaurate,dibutyltin dimaleate, dioctyltin dilaurate, dioctyltin dimaleate, andtin octylate; organotitanate compounds such as isopropyltris(isostearoyl) titanate, isopropyl tris(dioctylpyrophosphato)titanate, bis(dioctylpyrophosphato)oxyacetete titanate, and tetraalkyltitanate; organozirconium compounds such as tetrabutyl zirconate,tetrakis(acetylacetonato)zirconium, tetraisobutyl zirconate,butoxytris(acetylacetonato)zirconium, and zirconium naphthenate;organoaluminum compounds such as tris(ethyl acetoacetato)aluminum andtris(acetylacetonato)aluminum; organoinetallic catalysts such as zincnaphthenate, cobalt naphthenate, and cobalt octylate; and aminecatalysts, excluding organosilicon compounds, such as diethanolamine andtriethanolamine.

Preferably, this condensation reaction-promoting catalyst is added in anamount from 0.1 to 10 weight parts and more preferably in an amount from0.5 to 10 weight parts, in each case per 100 weight parts liquidalkoxysilyl-functional silicone resin. This condensationreaction-promoting catalyst may remain in the liquidalkoxysilyl-functional silicone resin even after the hydrolysis.

The liquid alkoxysilyl-functional silicone resin may be diluted withorganic solvent during the partial hydrolysis step of the presentmethod. Any organic solvent capable of dissolving the liquidalkoxysilyl-functional silicone resin can be used, and the particularorganic solvent should be selected based on the type and molecularweight of the liquid alkoxysilyl-functional silicone resin. The organicsolvent may be one solvent or a mixture of two or more solvents.Examples of useful organic solvents include alcohols such as methanol,ethanol, isopropanol, butanol, and isobutanol; esters such as ethylacetate, butyl acetate, and isobutyl acetate; ketones such as acetone,methyl ethyl ketone, and methyl isobutyl ketone; aliphatic hydrocarbonssuch as hexane, octane, and heptane; chlorinated organic solvents suchas chloroform, methylene chloride, trichloroethylene, and carbontetrachloride; aromatic hydrocarbons such as toluene and xylene; andvolatile silicones such as hexamethyldisiloxane andoctamethyltrisiloxane.

The present liquid alkoxysilyl-functional silicone resin, which is anequilibration reaction product from components (A) and (B) or fromcomponents (A), (B), and (D), is an organopolysiloxane comprising mainlytetrafunctional siloxane units (SiO_(4/2) units) and difunctionalsiloxane units (R³ ₂SiO_(2/2) units) although trifunctional siloxaneunits (R³SiO_(3/2) units) and/or the monofunctional siloxane units (R³₃SiO_(1/2) units) may also be present. These siloxane units are randomlydistributed within the molecule. Each R³ is a C₁ to C₁₀ substituted orunsubstituted monovalent hydrocarbyl group or a monovalent organic groupcontaining an aliphatically unsaturated bond. Examples of the C₁ to C₁₀substituted or unsubstituted monovalent hydrocarbyl group are asdescribed above for R. Examples of the monovalent organic groupcontaining an aliphatically unsaturated bond are as described above forR¹.

Generally, the liquid alkoxysilyl-functional silicone resin will containfrom 2 to 44 weight % alkoxy groups in the molecule and preferablycontains from 4 to 30 weight %. Alkoxy groups may be present in any ofthe aforementioned siloxane units. The liquid alkoxysilyl-functionalsilicone resin will generally have a viscosity at 25° C. of from 2 to500 mm²/s and preferably from 5 to 100 mm²/s. The weight averagemolecular weight of the liquid alkoxysilyl-functional silicone resinwill generally be no greater than 10,000 and is preferably no greaterthan 7,000.

Another embodiment of the present invention is a curable silicone resincomposition comprising a liquid alkoxysilyl-functional silicone resinand a curing catalyst. The liquid alkoxysilyl-functional silicone resinin the present embodiment is as described above. The curable siliconeresin composition cures rapidly at room temperature or upon heating. Thecuring catalyst can be a condensation reaction-promoting catalyst asalready described above or those equilibration polymerization catalyststhat exhibit a cure-promoting activity. Examples of usefulcure-promoting equilibration polymerization catalysts include stronglyacidic equilibration polymerization catalysts such as,trifluoromethanesulfonic acid and concentrated sulfuric acid. Thesecuring catalysts are used preferably in an amount from 0.05 to 15 weightparts and more preferably in an amount from 0.1 to 10 weight parts, ineach case per 100 weight parts of the liquid alkoxysilyl-functionalsilicone resin. When the liquid alkoxysilyl-functional silicone resin ismade using trifluoromethanesulfonic acid or concentrated sulfuric acidas component (C), or the condensation reaction-promoting catalyst usedfor hydrolysis remains present, a fresh addition of curing catalyst maynot be necessary since the aforementioned catalysts can function as thecure-promoting catalyst. However, when these are present in aninadequate amount, additional curing catalyst should be added insufficient quantity to make up the deficit.

The organic solvent may be allowed to remain when the liquidalkoxysilyl-functional silicone resin has been subjected to partialhydrolysis in organic solvent. In addition, organic solvent can beadmixed when dilution becomes necessary. When necessary or desired,chlorinated paraffin, solid paraffin, liquid paraffin, vaseline, and soforth can be added to the curable composition. In addition, thefollowing can be added as appropriate: pigments such as colorantpigments, filler pigments, and antirust pigments, as well asplasticizers, sag inhibitors, silane coupling agents, and antistainingagents. It is preferred that no more than 10 weight parts and morepreferably no more than 9 weight parts of these optional ingredients beadded, in each case per 100 weight parts liquid alkoxysilyl-functionalsilicone resin.

BEST MODE FOR CARRYING OUT THE INVENTION Examples

The invention is explained below through working examples, disclosed tofurther teach, but not limit, the invention, which is properlydelineated by the appended claims. The values reported for viscosity inthe examples were measured at 25° C. The contact angle versus water wasmeasured using a contact angle meter (CA-Z from Kyowa Kaimen KagakuKabushiki Kaisha).

Example 1

The following were introduced into a flask: 148 g of a mixture of cyclicdimethylsiloxanes (mixture of the tetramer to decamer) and 117.5 gmethyl polysilicate (average molecular weight=550, SiO₂ content=51weight %, viscosity=10 mPa·s) comprising the partial hydrolysis andcondensation product of tetramethoxysilane. 0.3 gtrifluoroinethanesulfonic acid was then added with stirring and theflask was heated to 70° C. and stirred for 8 hours. The generation of alarge number of peaks was observed when the reaction solution wasanalyzed by gas chromatography during the stirring period, whichconfirmed that the equilibration reaction between the cyclicdimethylsiloxane and methyl polysilicate had proceeded. Then, whileholding at 70° C., neutralization was carried out by bubbling in ammoniagas and the volatile fraction was thereafter stripped off under reducedpressure. After cooling, the neutralization salt that had been producedwas filtered off on filter paper to give 235 g liquidmethoxysilyl-functional silicone resin. This resin had a viscosity of 24mm²/s and a colorless and transparent appearance.

Analysis of this methoxysilyl-functional silicone resin by gaschromatography demonstrated that it was an equilibration reactionproduct with a distribution approximately from the diner to the 20-merand that it contained no more than 1 weight %octamethylcyclotetrasiloxane. The results of ¹³C-NMR and ²⁹Si-NMRanalyses demonstrated that this silicone resin was an organopolysiloxanewhose main skeleton comprised the difunctional siloxane unit((CH₃)₂SiO_(2/2) unit) and tetrafunctional siloxane unit (SiO_(4/2)unit) and that the silicone resin had a methoxy group content of 27weight %. Its weight average molecular weight as measured by GPC was3,500.

The liquid methoxysilyl-functional silicone resin produced as describedin this Example 1 was sealed in a glass bottle and held for 3 months atroom temperature. The appearance after this 3-month holding period wascolorless and transparent and showed no change from the appearanceimmediately after synthesis. No gel production was observed. Nosignificant change in viscosity was observed since the viscosity afterthe 3-month holding period was also almost the same as the viscosityimmediately after synthesis. These results demonstrated that thesilicone resin had excellent storage stability.

A curable silicone resin composition was prepared by adding 3 weightparts dibutyltin diacetate as curing catalyst to 100 weight parts of theliquid methoxysilyl-functional silicone resin prepared as describedabove and mixing at room temperature. The resulting composition wascoated on a glass slide and air-dried: a cured coating was formed after2 days. This coating was thoroughly cured and did not give a tackysensation when touched with a finger. The surface of this cured coatingwas smooth and gave a contact angle versus water of 100°, whichindicated an excellent water repellency.

Example 2

The following were introduced into a flask: 74 goctamethylcyclotetrasiloxane and 117 g methyl polysilicate (averagemolecular weight=550, SiO₂ content=51 weight %, viscosity=10 mPa·s)comprising the partial hydrolysis and condensation product oftetramethoxysilane. 0.2 g trifluoromethanesulfonic acid was then addedwith stirring and the flask was heated to 80° C. and stirred for 7hours. The generation of a large number of peaks was observed when thereaction solution was analyzed by gas chromatography during the stirringperiod, which confirmed that the equilibration reaction between theoctamethylcyclotetrasiloxane and methyl polysilicate had proceeded.Then, while holding at 80° C., ammonia gas was bubbled in for thepurpose of neutralization and nitrogen gas was bubbled in thereafter.After cooling the neutralization salt was filtered off on filter paperto give 186 g liquid methoxysilyl-functional silicone resin. This resinhad a viscosity of 10 mm²/s and a colorless and transparent appearance.

Analysis of this resin by gas chromatography demonstrated that it was anequilibration reaction product with a distribution approximately fromthe tetramer to the 20-mer and that it contained no more than 1 weight %octainethylcyclotetrasiloxane. The results of ¹³C-NMR and ²⁹Si-NMRanalyses demonstrated that this silicone resin was an organopolysiloxanewhose main skeleton comprised the difunctional siloxane unit((CH₃)₂SiO_(2/2) unit) and tetrafunctional siloxane unit (SiO_(4/2)unit) and that the silicone resin had a methoxy group content of 36weight %. Its weight average molecular weight as measured by GPC was1,500.

The liquid methoxysilyl-functional silicone resin produced as describedin this Example 2 was sealed in a glass bottle and held for 3 months atroom temperature. The appearance after this 3-month holding period wascolorless and transparent and showed no change from the appearanceimmediately after synthesis. No gel production was observed. Nosignificant change in viscosity was observed since the viscosity afterthe 3-month holding period was also almost the same as the viscosityimmediately after synthesis. These results demonstrated that thesilicone resin had excellent storage stability.

A curable silicone resin composition was prepared by adding 3 weightparts dibutyltin diacetate as curing catalyst to 100 weight parts of theliquid methoxysilyl-functional silicone resin prepared as described inthis Example 2 and mixing at room temperature. The resulting compositionwas coated on a glass slide and air-dried: a cured coating was formedafter 3 days. This coating was thoroughly cured and did not give a tackysensation when touched with a finger. The surface of this cured coatingwas smooth and gave a contact angle versus water of 99°, which indicatedexcellent water repellency.

Example 3

The following were introduced into a flask: 81 g of a mixture of cyclicdimethylsiloxanes (mixture of the tetramer to decamer), 1116 g methylpolysilicate (average molecular weight=550, SiO₂ content=51 weight %,viscosity=10 mPa·s) comprising the partial hydrolysis and condensationproduct of tetramethoxysilane, and 27 gγ-methacryloxypropyltrimethoxysilane. 0.2 g trifluoromethanesulfonicacid was then added with stirring and the flask was heated to 75° C. andstirred for 8 hours. The generation of a large number of peaks wasobserved when the reaction solution was analyzed by gas chromatographyduring the stirring period, which confirmed that the equilibrationreaction between the siloxane and methoxy groups had proceeded. Aftercooling to room temperature, neutralization was carried out by bubblingin ammonia gas and the neutralization salt thereby produced was filteredoff across filter paper. The volatiles were subsequently removed bystripping by heating under reduced pressure leaving 246 g liquidmethoxysilyl-functional silicone resin bearing the γ-methacryloxypropylgroup. This resin had a viscosity of 7 mm²/s and a colorless andtransparent appearance.

Analysis of this resin by gas chromatography demonstrated that it was anequilibration reaction product with a distribution approximately fromthe trimer to the 20-mer and that it contained no more than 1 weight %octamethylcyclotetrasiloxane. The results of ¹³C-NMR and ²⁹Si-NMRanalyses demonstrated that this silicone resin was an organopolysiloxanewhose main skeleton comprised the difunctional siloxane unit((CH₃)₂SiO_(2/2) unit), trifunctional siloxane unit(CH₂═C(CH₃)COOC₃H₆SiO_(3/2) unit), and tetrafunctional siloxane unit(SiO_(4/2) unit) and that the silicone resin had a methoxy group contentof 35 weight %. Its weight average molecular weight as measured by GPCwas 1,200.

The liquid methoxysilyl-functional silicone resin produced as describedabove in this Example 3 was sealed in a glass bottle and held for 3months at room temperature. The appearance after this 3-month holdingperiod was colorless and transparent and showed no change from theappearance immediately after synthesis. No gel production was observed.No significant change in viscosity was observed since the viscosityafter the 3-month holding period was also almost the same as theviscosity immediately after synthesis. These results demonstrated thatthe silicone resin had excellent storage stability.

A curable silicone resin composition was prepared by adding 5 weightparts dibutyltin diacetate as curing catalyst to 100 weight parts of theliquid methoxysilyl-functional silicone resin prepared as described inthis Example 3 and mixing at room temperature. The resulting compositionwas coated on a glass slide and air-dried: a cured coating was formedafter 3 days. This coating was thoroughly cured and did not give a tackysensation when touched with a finger. The surface of this cured coatingwas smooth and gave a contact angle versus water of 100°, whichindicated excellent water repellency.

Example 4

50 g methanol and 50 g of the liquid methoxysilyl-functional siliconeresin prepared in Example 1 were mixed. To this mixture was added 0.6 gtetra-n-butyl orthotitanate and then a mixture of 0.3 g water and 1 gmethanol and partial hydrolysis was subsequently carried out by mixingfor 1 hour. The post-hydrolysis methoxy group content was 25 weight %. Acured coating was formed after 2 days when the resulting partialhydrolyzate was coated on a glass slide and air-dried. This coating wasthoroughly cured and did not give a tacky sensation when touched with afinger. The surface of this cured coating was smooth and gave a contactangle versus water of 100°, which indicated excellent water repellency.

Comparative Example 1

The following were introduced into a flask: 148 g of a mixture of cyclicdimethylsiloxanes (mixture of the tetramer to decamer) and 30 gmethyltrinethoxysilane. 0.15 g trifluoromethanesulfonic acid was thenadded with stirring and the flask was heated to 80° C. and stirred for 6hours. The generation of a large number of peaks was observed when thereaction solution was analyzed by gas chromatography during the stirringperiod, which confirmed that the equilibration reaction between thesiloxane and methoxy groups had proceeded. Then, after cooling to roomtemperature, neutralization was carried out by bubbling in ammonia gasand the neutralization salt thereby produced was filtered off acrossfilter paper. The volatiles were subsequently removed by stripping byheating under reduced pressure to give a liquid methoxysilyl-functionalsilicone resin. This silicone resin was an organopolysiloxane whose mainskeleton comprised the difunctional siloxane unit ((CH₃)₂SiO_(2/2) unit)and trifunctional siloxane unit (CH₃SiO_(3/2) unit).

A silicone resin composition was prepared by adding 5 weight partsdibutyltin diacetate as curing catalyst to 100 weight parts of theliquid methoxysilyl-functional silicone resin prepared as described inthis Comparative Example 1 and mixing at room temperature. When theresulting composition was coated on a glass slide and air-dried, it wasstill tacky when touched with a finger even after 2 days, whichconfirmed that the cure was inadequate.

INDUSTRIAL APPLICABILITY

The present alkoxysilyl-functional silicone resins are liquids at roomtemperature and have excellent long-term storage stability both in asolventless state and when diluted with organic solvent. The siliconeresins obtained by equilibrating components (A) through (D) containaliphatically unsaturated bonds in the molecule, and therefore offer theadvantage of high reactivity with radical polymerization-reactiveorganic polymers, e.g., acrylic resins. A preferred preparative methodremoves the volatile low-molecular-weight siloxanes that includes thecyclic diorganosiloxane tetramer, and therefore affords a highly curablesilicone resin. Moreover, since the removed cyclic diorganosiloxane canbe reused as a starting material in the equilibration reaction, thepreparative method has the advantage of enabling continuous productionof the alkoxysilyl-functional silicone resins and making possible asubstantial reduction in the amount of waste generation.

The present curable silicone resin composition can form a smooth,water-repellent film on the surface of a variety of inorganic andorganic substrates. In particular, the curable silicone resincomposition is useful as a coating agent for such inorganic materials asglasses, ceramics, and metals.

1. A method of forming liquid alkoxysilyl-functional silicone resins,the method comprising reacting (A) a polydiorganosiloxane, (B) an alkylpolysilicate, and (D) a functional alkoxysilane with the general formulaR¹SiR_(n)(OR²)_(3-n), wherein each R is a substituted or unsubstitutedC₁ to C₁₀ monovalent hydrocarbyl group, R¹ is a C₁–C₁₀ monovalentorganic group having an aliphatically unsaturated bond, each R² is a C₁to C₁₀ alkyl group, and n is 0 to
 2. 2. The method of claim 1 wherein(A) is selected from the group consisting of (i) a straight chainpolydimethylsiloxane and (ii) a cyclic polydimethylsiloxane and (B) isselected from the group consisting of (a) methyl polysilicate and (b)ethyl polysilicate.
 3. The method of claim 1, wherein (B) is a mixtureof polysiloxanes ranging from dimer to 100-mer.
 4. The method of claim1, where (C) is an acid catalyst.
 5. The method of claim 1, where themethod further comprises thermally removing low-molecular-weightvolatile siloxanes so no more than 1 weight % cyclic tetramer remains.6. The method of claim 5, wherein the method further comprises partiallyhydrolyzing the liquid alkoxysilyl-functional silicone resin to adjustthe amount of alkoxy groups.
 7. The liquid alkoxysilyl-functionalsilicone resin prepared by the method of claim
 1. 8. A liquidalkoxysilyl-functional silicone resin obtained by the method of claim 1comprising tetrafunctional siloxane units (Si04/2 units) anddifunctional siloxane (R³ ₂SiO_(2/2)) units, where each R³ is selectedfrom the group consisting of (i) a C₁ to c₁₀ substituted monovalenthydrocarbyl group, (ii) an unsubstituted monovalent hydrocarbyl group,and (iii) a monovalent organic group containing an aliphaticallyunsaturated bond.
 9. The liquid alkoxysilyl-functional silicone resin ofclaim 8 where the liquid alkoxysilyl-functional silicone resin has aviscosity at 25° C. of from 2 to 500 mm²/s, a weight average molecularweight no greater than 10,000 and from 2 to 44 weight % alkoxy groupsper molecule.
 10. A curable alkoxysilyl-functional silicone resincomposition comprising the liquid alkoxysilyl-functional silicone resinof claim 7 and a curing catalyst.
 11. The method of claim 1, wherein (A)is selected from the group consisting of (i) a straight chainpolydimethylsiloxane and (ii) a cyclic polydimethylsiloxane and (B) isselected from the group consisting of (a) methyl polysilicate and (b)ethyl polysilicate.
 12. The method of claim 1, wherein (B) is a mixtureof polysiloxanes ranging from dimer to 100-mer.
 13. The method of claim2, wherein (B) is a mixture of polysiloxanes ranging from dimer to100-mer.
 14. The method of claim 2, where (C) is an acid catalyst. 15.The method of claim 3, where (C) is an acid catalyst.
 16. The method ofclaim 12, where (C) is an acid catalyst.
 17. The method of claim 13,where (C) is an acid catalyst.
 18. The method of claim 1, where (C) isan acid catalyst.